The incorporeal enemy enters the heart of man through satiety and drunkenness — this can be felt by anyone who is observant.
This is the reason why, with the growth of drunkenness, the inclination to drunkenness increases so terribly (because the power of the enemy over the man increases)–this is why you notice in drunkards a power involuntarily drawing them to satisfy their passion or their inward craving for wine. The enemy is in the hearts of these unhappy people.
How can the demon of drunkenness be driven out? By prayer and fasting. The enemy enters the hearts of men because they have given themselves up to a carnal mode of life–to gluttony, and because they do not pray.
It is, therefore, natural that he can be driven out from them by opposite means–that is, by prayer and fasting.
— St John of Kronstadt